Extracellular adenosine triphosphate has been shown to regulate a variety of biological processes including non-vascular smooth muscle contraction (M. Maguire and D. Satchell, J. Pharmacol. Exp. Ther. 211, 626-631 (1979); C. Brown and G. Burnstock, Eur. J. Pharmacol. 69, 81-86 (1981)) and vascular tone (G. Burnstock and C. Kennedy, Circ. Res. 58, 319-330 (1986); D. Haeussinger et al., Eur. J. Biochem. 167, 65-71 (1987)), platelet aggregation (G. Born and M. Kratzer, J. Physiol. (Lond.) 354, 419-429 (1984)), neurotransmission (G. Burnstock, Nature, 229, 282-283 (1971); G. Burnstock and P. Sneddon, Clin. Sci. 68 (Suppl. 10), 89s-92s (1985)), and cellular ion transport (G. Burgess et al., Nature 279, 544-546 (1979); D. Galacher, Nature 296, 83-86 (1982)) and secretory activities (J. Chapal and M-M. Loubatieres-Mariani, Br. J. Pharmacol. 73, 105-110 (1981); J. Pearson et al., Biochem. J. 214, 273-276 (1983)). These effects are mediated by specific purinergic receptors which respond to ATP or other nucleotides present in the extracellular millieu (J. Gordon, Biochem. J. 233, 309-319 (1986)).
Purinoceptors have been functionally identified in rat pulmonary epithelia in studies of regulation of alveolar Type II surfactant phospholipid secretion (W. Rice and F. Singleton, Br. J. Pharmacol. 89, 485-491 (1986)). To our knowledge these receptors have not been reported in human airway epithelial cells. Because ion transport appears to be regulated by purinergic receptor stimulation in other epithelia (Burgess et al., supra (1979); Gallacher, supra (1982)), we investigated several features of the effect of extracellular nucleotides on the ion transport activities of human airway epithelium.
Purinergic receptor regulation of ion transport might have potential therapeutic benefit in lung diseases characterized by abnormalities in epithelial ion transport, e.g., cystic fibrosis. In cystic fibrosis the airway epithelial dysfunction is expressed in part by defective regulation of Cl.sup.- ion transport by secretagogues that regulate the apical cell membrane Cl.sup.- channel by cAMP-dependent or protein kinase C dependent mechanisms (R. Boucher et al., J. Clin. Invest. 78, 1245-1252 (1986); R. Boucher et al., J. Clin. Invest. 84, 1424-1431 (1989); J. Riordan et al., Science 245, 1066-1073 (1989); J. Rommens et al., Science 245, 1059-1065 (1989)). Induction of Cl.sup.- secretion by CF airway epithelia in vivo might help liquify the relatively dehydrated, thick airway surface liquid that characterizes this disease. We therefore tested whether nucleotides would bypass regulatory defects in CF airway epithelia and induce Cl.sup.- secretion at rates similar to those of normal airway cells. The present invention is based upon this investigation.